1. Field of the Invention
This invention relates to a handling apparatus used to transfer carriers which store a plurality of semiconductor wafers or liquid crystal substrates, for example, and also to a method of transferring the carriers by using the handling apparatus.
2. Description of the Related Art
In the process of manufacturing semiconductor devices, semiconductor wafers are transferred in units of lots from one process to another. In other words, wafers are not transferred one by one from one process to another, but instead, a plurality of wafers are placed in box-shaped carriers and transferred in units of lots.
In general, a stocker, for temporary storage of a large number of carriers, is installed beside each unit or group of units such as processing units, wafer testing units, and the like, the purpose of this being to enable the wafers--in units of lots--to be processed in batches. Stated another way, since the processing time differs considerably from one type of processing unit to another, it is therefore necessary to provide means for temporary storage of carriers waiting to undergo processing or to be sent to the next process.
The flow of carriers will now be described briefly as follows:
The carriers are carried by robot from the preceding processing line to a stocker, which is made up of a number of storage compartments, and are stored there temporarily. Then, when desired, the carriers are taken out, one by one, from the storage compartments, and transferred to a processing unit. Then, after being processed by the processing unit in question, the processed wafers are returned to the carrier from which they were removed.
In putting the carriers in and taking them out of the stocker, the carriers are normally first placed on a loading/unloading table and then, they are transferred into and out of the storage compartments by a handling apparatus provided with a traveling and a holding function. To be more specific, the handling apparatus selects the storage compartment of the stocker, identified by address, to which it is going to store the carrier or from which it is going to take the carrier.
Since semiconductor wafers have a hyperfine pattern formed thereon, the wafer surface can easily be damaged even by very fine dust particles. In order to minimize contamination of the wafer surface by dust, it is essential that all handling of the wafers be conducted in a clean room. In the clean room, clean air is made to flow from the ceiling toward the floor to keep the room at a high level of cleanliness (with a smaller number of floating dust per unit volume).
A conventional handling apparatus, however, has a larger number of driving axes and a complicated structure, and thus, when a carrier is handled by such a apparatus, dust is produced by the drive mechanism, and notably degrades the cleanliness of the room. In order to handle semiconductor wafers of a high density integrated circuit pattern, an ultra-high level of cleanliness is required of the clean room. Using a conventional handling apparatus, this requirement cannot be met.
The conventional handling apparatus is structured such that it, a carrier from above and the carrier storing section moves at a higher position than the carrier, thus disturbing the laminar air flow and degrading the cleanliness of the room. Furthermore, since the conventional handling apparatus has a complicated structure with a large number of driving axes, this means a high equipment cost and an economic disadvantage.